A new standard for compressing 5.1 multichannel audio combines the quality of …

Share this story

Anyone who owns a nice home theater setup (or has friends who do) has experienced the immersion of 5.1 surround sound. The combination of two forward stereo speakers, a center speaker, two rear speakers, and a subwoofer provide a depth of sound that can convincingly simulate a three-dimensional environment.

The standard for 5.1 sound, Dolby Digital (also known as AC-3) is used in movie theaters, DVDs, and some game consoles. However, the codec used for AC-3 is not as efficient as more modern codecs used to compress music on computers. For several years now, various companies involved in the development of compression codecs have been working on combining these codecs with 5.1-channel audio to create a new sound standard.

Last year, the Fraunhofer company in Germany demonstrated MP3 Surround, and even released an MP3 Surround portable player to go with it. Now a consortium of companies, including Fraunhofer, Agere Systems Inc., Coding Technologies GmbH, and Philips Applied Technologies, have taken the idea a step further with a new standard called MPEG Surround.

The technology, which adds the MPEG-4 Advanced Audio Codec (AAC) and MPEG-4 HE AAC (also known as aacPlus) to the list of supported codecs, was demonstrated this week at the Audio Engineering Society Expo in Paris, France.

The addition of AAC and HE AAC codecs adds "only a negligible increase in data rate," said Bernhard Grill, head of the audio department at the Fraunhofer Institute for Integrated Circuits IIS. Replacing Dolby Digital 5.1 with MPEG surround saves "roughly 2.5 times [the] bandwidth," he added.

It should be noted that many press outlets erroneously call AAC "Apple's codec"—while it is used by iTunes and the iPod, it is an open standard that is essentially an evolution of MP3, and it is only Apple's Digital Rights Management software that is exclusive to the iPod and iTunes.

So is the new standard likely to find any traction? Owners of existing home theaters are unlikely to upgrade their equipment merely to save on bandwidth, and owners of portable music devices usually listen to them via headphones, which do not benefit from 5.1 sound. Does this make MPEG Surround merely a solution in search of a problem?

One area where it may find some uptake is in digital television broadcasting, where service providers are anxious to find ways to squeeze out more channels and more features with the same bandwidth. The new technology does not require broadcasters to send separate audio streams for stereo and 5.1 surround, as it can decode a single stream into either format. It will, however, require new MPEG Surround decoder chips, which are not yet available. Grill said that "a high-end DSP available on the market today should be able to handle the task."

MPEG Surround is set to become an international draft standard this July.